1. Field of the Invention
The invention relates to an installation and a process for maintaining at desired temperature values, in any circumstances, a coal preheating installation comprising at least one drying chamber fed by a fluidisation agent, a combustion chamber having a neutral combustion burner producing a hot neutral gas serving as entrainment agent and as drying and fluidisation agent, and means for regulating the supply of liquid or gaseous fuel to the burner which are controlled by means for measuring the temperature in the drying chamber.
2. Description of the Prior Art
In the technique of charging coke fines by preheating the fines, it is known to prepare a charge of coal by grinding and drying in a fluidisation reactor known as a grinder-drier, in which a grinding member rotates and from which the suitably ground coal, heated to between 100.degree. C. and 260.degree. C., is entrained into a waiting hopper. In an installation of this kind it may be necessary to interrupt the supply of coal to the grinder-drier, for example because of an incident upstream or downstream of that apparatus. However, if the burner is not then extinguished there is a risk that the temperature of the installation will rise to an excessive value, resulting in the coking of the wet coal stagnating in the supply part, so that there will be a danger that the installation cannot be started up again under normal conditions.
For solving this problem it has already been proposed in French Patent Application No. 75,25425 (Publication No. 2,281,971) to reduce the power of the burner to its minimum value and to inject, preferably upstream of the grinder-drier, water whose heat of vaporisation will absorb the heat produced by the burner working at its minimum power, thereby eliminating the risk of coking.
However, a solution of this kind is not without disadvantages.
One disadvantage of the above solution is that the refractory materials are damaged by too abrupt cooling by water in one of the hottest zones of the installation. Furthermore, the amount of water used must be relatively large, because owing to the fact that the gases coming from the combustion chamber must be neutral the flexibility of regulation of the burner is limited to a range between its nominal power and about one-third of that power. Fuel is therefore consumed entirely wastefully, because in the interim period one-third of the nominal power of the burner is used for vaporising water.